1. Field of the Invention
This invention relates to the field of a rotary code switches and more particularly to the improvement of a contact member of a rotary code switch of the dual-in-line-package type (hereinafter called DIP rotary code switch).
2. Description of the Related Art
A rotary code switch having a "dual-in-line-package" structure is small and has been developed for installation on a printed circuit board equipped with electronic components and control devices.
A conventional DIP rotary code switch includes: a base made of insulative material in which a circuit board is embedded; a plurality of terminals which may comprise a common terminal, a pull-up terminal and a plurality of output terminals arranged on the circuit board; a plurality of contact members each having an inverted V-shape comprised of two legs and an apex arranged underneath a rotor which is rotatably mounted within a cavity formed by a housing and the base. A disc or substrate is mounted for rotation with the rotor. Various patterns of conductive material devised to meet the desired purposes of the switch are arranged on the lower surface of the disc or substrate which is rotatably mounted on a boss of the base so as to be simultaneously rotatable with the rotor.
When the rotor and the disc rotate, the patterns of conductive material of the disc may intermittently contact the apex head of the contact member whose two legs are mounted in longitudinal slits of the base respectively to touch conductor elements arranged on a circuit board which is embedded in the base and to which plate terminals are connected, thereby resulting in electrical connection or disconnection of the plate terminals.
Such a rotary code switch has been invented by the present inventor and is disclosed in Japanese Provisional Patent Publication No. 114713/1984. The switch is provided with plate terminals comprising a common terminal, a pull-up terminal and a plurality of output terminals. The arrangement of the plate terminals of the prior art switch is as follows:
a same number of resistance elements and diodes as there are output terminals are, respectively, disposed between the pull-up terminal and the out-put terminals or a same number of diodes as there are output terminals are disposed, respectively, between the common terminal and the out-put terminals. In an IC logical circuit, each signal line is connected to a power line (Vcc) through a resistance for securing a threshold level. Such a system is referred to as "pull-up", and the resistance is called "pull-up resistance". In logics, meanwhile, a common terminal of a switch can be connected to a power line (Vcc) and thus resistance is grounded. The system is referred to as "pull-down".
The contact member adopted by the DIP rotary code switch described heretofore, has an inverted letter V-shaped having two legs and an apex from which the legs extend. The legs are mounted in a longitudinal slit disposed in the base and touch conductor elements arranged on a circuit board embedded in the base and are located underneath the disc which rotates with the rotor. The apex of the contact member slidably engages conductive printed patterns disposed on the undersurface of the disc, whenever the disc is rotated with the rotor. Because the two legs of the contact member are positioned in a longitudinal slit defined in the base, the contact member is shiftable lengthwise within the slit and the apex tends to sway back and forth whenever the disc rotates with its undersurface contacting the apex. Therefore, it is difficult to maintain appropriate contact between the conductive patterns arranged on the undersurface of the disc and the contact member, thereby, resulting in a reduction in the electrical efficiency of the switch.